Method of and means for synchronizing wave generators



June 4, 1946. A. v. BEDFORD 2,401,405

METHOD OF AND MEANS FOR SYNCHRONIZING WAVE GENERATORS I Filed May 20, 1944 3 Sheets-Sheet 2 Zw aum/ffm: 7mm# f Riff/v5 P /FFE/Pfmnrfa (www 501.5 TED 5 YNC/.

WH VE 1N VEN TOR.

5 Sheets-Sheet 3 A. V. BEDFORD Filed May 20, 1944 AIAA.

`lune 4, 1946.

METHOD oF AND MEANS FOR sYNcHRoNIzING WAVE GENERATORS IN1/mole.

1451@ BY l Arme/Vn Patented June 4, 1946 METHOD F AND MEANS FOB SYNCHBO- NIZIN G WAVE GENERATOR Alda V. Bedford, Princeton, N. J., or to Badio Corporation of America, a ation of Delaware The present invention relates to wave transmission systems and more particularly to an improved method of and means for synchronizing a plurality of wave generators.

Theinvention, by way o example. will be described hereinafter as an improvement in a secret telecommunication system of the type described in applicants copending U. S. application Ser. No. 514,351, filed December 15, 1943. Said copending application discloses and claims a system wherein, for example, a speech signal comprising a complex wave S is modiiled by means of a. coding signal comprising a complex wave K in a manner whereby the instantaneous ordinates of the resulting coded signals are the product SK of the corresponding instantaneous ordinates of the speech signal and the coding signal. The resulting unintelligible coded signals are transmitted by any conventional means to a receiver wherein the coded signals are combined with decoding signals generated in the receiver and having instantaneous ordinates corresponding to the reciprocals of the corresponding instantaneous ordinates of the coding signal component of the transmitted signal. The ilnal signals, therefore, are derived from the product of the transmitted signal SK and the decoding signal l/K. The coding and decoding signal generators, at the transmitter and receiver, respectively, are disclosed in said copending application as synchronized by any conventional auxiliary synchronizing system.

The instant invention comprises an improved method of and means for synchronizing the coding and decoding wave generators by means of special synchronizing pulse signals each comprising a rst signal pulse immediately followed by a second signal puise ol opposite polarity,

p which pulses may be superimposed upon the coded signals SK. At the receiver, the reversal in polarity between the two synchronizing pulses is employed to synchronize the decoding wave generator. -It should be understood that while the present invention is described with reference to the type of system disclosed in said copending application, it also may be employed for synchronizing any known types of wave generators wherein synchronizing wave control pulses may be employed. and wherein relatively precise synchronism is desirable.

Among the objects of the invention are to provide an improved method of and means for synchronizing a plurality of wave generators. Another obiect of the invention is to provide an improved method of and means for synchronizwaves generated by a plurality oi separately pulseexcited delay networks. Another object of the invention is to provide an improved method of and means for synchronizing secret telecommunication systems.A An additional object is to provide an improved synchronizing pulse generator. A further object is to provide an improved receiving network for synchronizing a local wave generator with a remote wave generator in response to synchronizing signals combined with signals received from said remote wave generator. Another object is to provide an improved synchronizing system wherein synchronizing signals comprising a tlrst pulse immediately followed by a second pulse of opposite polarity are transmitted to a receiver responsive to the reversal in polarity between said pulses.

The invention will be described in greater detail by reference to the accompanying drawings f of which Figure 1 is a schematic block circuit diagram of a complete secret telecommunication system employing a preferred embodiment of the invention, Figure 2 is a series of graphs illustrating the circuit operation of the transmitting portion of the system shown in Figure 1, Figure 3 is a series of graphs illustrating the operation of the receiver portion o! the circuit illustrated in Figure 1, Figure 4 is a schematic circuit diagram of the wave multiplier forming a portion of the circuit of Figure 1, and Figure 5 is a schematic circuit diagram of a wave reciprocal circuit forming a portion of the system shown' in Figure 1. Similar reference characters are applied to similar elements throughout the drawings.'

Coding wave generator Referring to Figure l, the coding wave generator employed for both transmitting and receiving coded speech signals comprises a conventional free-running multivibrator circuit I which generates pulses at a rate. for example, of one hundred pulses per second. A typical multivibrator of this type, the frequency of which may be controlled by recurrent applied control pulses, is described in U. S. Patent 2,266,526, granted to E. L. C. White on December 16, 1941. It should be understood that pulses of either polarity may be applied in any known manner to key. the multivibrator, and that similarly output pulses of either polarity may be derived therefrom. The generated pulses are applied to the input of a. conventional delay network 2 comprising a plurality of series inductors 3. 5, 6, 9. II and a. plurality of shunt capacitors 6. 8, I0, I2, I4.

ing more precisely than was heretofore possible The remote terminals ofthe resultant pulse delay input of the delay network 2 provide similarpulses at the junction of each oi' the succeeding series inductors I, l, l, l. I I wherein each succeeding pulse is delayed a predetermined amount with respect to pulses occurring at other prior network terminals. A complex coding wave thus may be obtained in response to each pulse applied to the delay network by combining in either polarity din'erently delayed pulses derived from a plurality of such predetermined points along tho delay network.

Separate isolating resistors Il, I'I, i. 2|, 2l, 25 each have one terminal connected to diii'erent points along the delay network, and have their remaining terminals connected to separate movable contacts of a plurality of single-pole doublethrow switches 21, 2s, 3|, n, Il. Il. The corresponding fixed contacts o! the several switches :ire connected together to provide two lines ll, 4|, which are terminated through resistors 43, u, respectively. to ground. The remaining terminal of the line ll is connected through a coupling resistor Il to one ilxed contact Ti o! a ilrst "transmit-receive single-pole, double throw switch 49. The remaining terminal of the second line 4l is connected through a polarity-reversing ampliiier 5I and a second coupling resistor Il to said first fixed contact Ti of the ilrst "transmitreceive" switch I9. Thus each of the 100 pulses per second, derived from the multivibrator l and applied to the input oi the delay network 2. provides a plurality oi pulses of either polarity occurring at predetermined intervals during each one-hundredth second period, as determined by 'the points of connection to the delay network and the arrangement of theswitches 21, 2l. ll, Il, Il, l1. Therefore, a very complex coding wave may be applied tothe first ilxed contact Ti of the ilrst transmit-receive" switch Il, merely by selecting the desired arrangement of the pulse selecting switches. It should be understood that the total delay provided by the pulse delay network should be at least slightly less than the pulse period o! the multivibrator I in order that only one pulse may be traveling along the delay4 network at any predetermined instant.

In the typical secret telecommunication system described in applicants copending application identiiled heretofore, the coding signal generator includes a delay network having Il sections and a plurality of sequential switches which may be preset to any desired code and selectively actuated by a clock mechanism to change the code continuously or at predetermined desired intervals. Identical coding Signal generators are employed at both the transmitter and receiver in such a secret telecommunication system. By means of simple transmitreceive"-switchea the coding signal either is combined with the speech signal for transmitting a. coded wave, or reciprocal values oi' the coding Sinal are derived from a reciprocal circuit responsive to the coding signal generator and are combined with the received coded signal to decode said received signal. Much of the decoding apparatus including the generator 4 Iorthacodesignalisidenticaltotheooding paratus. Hence.bymeansofthesimple mit-receive switches. the various elements theapparatusmaybeemnlondatdiilesenttim. for dual Purposes in a single unit for transmittingorreceivingtheoodadlhnah.

` Reterringtollgurland2, beemployedasaooding switching the movable contacts of each of the single-pole,

double-throw transmit-receive switches included therein to engage the nxed contact. Ti, Ts, Ts. T4. Ts, Ta corresponding to the transmit condition. Signals derivedJor example, from a microphone Il, which may be fed through a speech ampliiier, not shown, are applied through a second transmit-receive switch I'I to me input circuit of a wavemultiplier Il. which will be described in detail hereinarter by reference to Figureiotthe drawings. Godingsianalairom the coding signal generator described heretolora,

are applied, through the rst switch 4l, to a ncond input circuit of said wave multiplier Il, whereby coded signals BK having instantaneous ordinates corresponding to the producto o! the corresponding instantaneous ordinates o! the speech signal B and the coding lilnal X an applied through a third "transmit-receive" switch 6| to one input circuit of a first mixer circuit which may comprise any conventional network wherein applied signals are combined algebraically.

Transmitter synchronizing palas generator Regularly recurrent pulses indicated by the graph (a) of Figure 2 are derived, for example. from the seventy-ninth tap on the delay network 2 and applied to a conventional thennionic tube amplitude limiter circuit l1, which clips the wave (a) at the level D to derive individual limihd pulses represented by graph (b) o! Figure 2. nie limited pulses (b) are applied through a fourth "transmit-receive" switch Il to key a second multivibrator Il to derive a negative substantially square-wave pulse killustrated by graph (c) of Figure 2. 'I'he negative square wave pulse (c) is applied through a fifth "transmit-receive" switch Il to a second input circuit oi' the ilrst mixer circuit Il, and is applied through a sixth transmitreceive switch 1I to key a third multivibrator 'I1 which generates a positive square wave pulse indicated by the graph (d) oi Figure 2. It will be understood that the positive square wave pulse (d) will be initiated at the termination of the negative square wave pulse (c) in a manner well known in the multivibrator art. The podtive square wave pulse (d) is applied to a third input circuit of the mixer circuit I3 whereby the coded signal SK, the negative square wave pulse (c) and the positive square wave puise (d) are combined to provide a communication signal including the coded wave SK and-the synchronizing signal comprising a negative square wave pulse immediately followed by a positive square wave pulse. It should be understood that, if desired, the. synchronizing signal may comprise a positive pulse followed by a negative-pulse since multivibrators may be keyed by, and can provide. pulses oi' either polarity, providing proper connections thereto are provided in a manner known in the art. 'I'he combined coded signal and synchronizing signal derived from the mixer Il will have a wave form, for example, of the type illustrated in graph (l) Mossos ceedlng pulse which will b'e progressivelydelayed along the delay network. Since the first multivibrator' i is'keye'd by the pulse from the third multivibrator I1 immediately preceding the time for the generation of a normal pulse by said rst multivibratonit -will be'seen'that the'coding wave generator will be. self-running, and will be maintainedl ata substantially constant frequency.` since the pulse rate therethrough will be substantially vdependent upon the time delay of the successive pulsesapplied to the delay net'- work 2. If'ior any reason the first multivibrator i I is'not'properly keyed bythe third multivi-` brator 'IIfthe multivibrator will merely generatea pulse (e') which will be applied to the delay `network vZat a slightly later interval.A

The slightly delayed 'pulse' upon reaching the seventy-ninth tap of the delay network therefore will key the second and third multivibrators inthe manner described heretofore and provide a new set of synchronizing pulses which will actuate the ilrst multivibrator *I in synchronism thereafter.

'Ihe coded signals 'SK combined with the synchronizing pulses (c) and (d) are applied to a second limiter T9 whereby the 4high amplitude portions I of the synchronizing signal are clipped to a maximum level II indicated by the dash lines in graph (f). of Figure 2. The thus limited combined coded and synchronizing signals are applied as a communication signal to a conventional radio transmitter 8I which includes a transmitting antenna 83.

v Coding signal receiver In order to convert the circuit thus described to operate as a coded signal receiver, the movable contacts of each of the transmit-receive switches t9, 51, 6I, 69, 13 and 'I5 are switched to the corresponding fixed contactsvDi, D2, Da, D4, Ds, De, corresponding to the receive condition. The combined coded signal and synchronizing signals transmitted from the transmitter 8l are "smeared and phase-shifted somewhat in transmission t resemble the solid portion :n of theg'raph (f) of Figure 2, and as received by means of a conventional radio receiver 85 are applied to a lconventional wave difierentiating network 81 which may be of any type well known in the art. For example, a wave may be diiferentiated by applying it to a network comprising a small series capacitor and a shunt resistor. The transmitted signal (f) of Figure 2 after being differentiated at thereceiver resembles the graph (g) of Figure 3 wherein a relatively large pulse P occurs at an instant correspondingto the reversal in polarity between the received synchronizing negative and positive pulses and wherein low frequency components are substantially removed from the pulse P. It should be understood that instead of diil'erentiating the received signal. it may be treated in any other known manner to derive a pulse in response to thereversal in polarity of the negative and positive synchronizing pulses.

The receiver first multivibrator I being free running, as described heretofore, the delay network 2 will provide recurrent pulses at its seventyin the transmitting circuit. Thediiferent pulso eighth tap which will third limiter B9 to provide limited pulses represented by the graph (n) `of Figure 3. The thus limited pulses (h) are applied to key a roux-thv multivibrator which generates a relatively long. leaking pulse inustrad in mph-u) or i Figure 3.A The longblankingpulse (i) is applied to a blanking circuit iwhichblanks out por tionspf the received signal, as will be explainedm greater detaiihereinafter. y

.-f.; Receiver synchronizing circuits Similarly. cachot the recurrent pulses'derived fromthe eightieth tap of the delay network 2 are appliedto a fourth limiter y which clips the upper portion of the applied pulse as explained heretofore with respect to pulse (b), to provide a shortpulse illustrated by graph (1l-vof Figure 3. The glimited pulse. (i) is applied through the fourthf'transmit-receive" switch 6 9 to key the second multivibrator1I to provide a relatively long positive square wave pulse (k). It will be noted'that the positive pulse (k) isvof relatively longer duration than the negative pulse (c) previouslydescribed as generated by the second multivibrator 'II when said multivibrator is employed polarity and duration may be accomplished. in any well :known manner by changes lprovided in the multivibrator circuit constants and the connections thereto,A when the multivibrator is switched from the transmitting" to the"re ceiving condition.

Thepositive square wave pulse (k) derived from the `.second multivibrator. 'Ii is applied through the fifth transmit-receive switch 'i8 to a second mixer circuit el, to which also is applied the differentiated wave (g) derived from the differentiating circuit 81. The thus mixed signals illustrated by lgraph (l) of Figure 3 include a pulse peak (l)` which corresponds-in time to the occurrence of the large positive pulse P of the differentiated received wave (y). As explained heretofore, the pulse P corresponds to the reversal in polarity of the received synchronizing negative and positive pulses. The wave (l) derived from the second vmixer circuit Si is applied to a' fifth limiter 99 which clips the mixed signal atfa level (y) to provide in its output circuit a short somewhat triangular pulse, illustrated bygraph (m) of Figure 3.

The triangular pulse (m) is applied through the sixth "transmit-receive switch I5 to key the third multivibrator Il to provide a positive pulse represented by graph (n) of Figure 3 which is applied"jfto ll rey the rst multivibrator I as describedh'eretofore with respect to the pulse (d) in the transmitting network. It should be understood that,'ii' 4 desired for extremelyprecise synchronism, the'pulse (m) may be changed from triangular tosq'uare wave shane by clipping vat a low level vand then by amplifying the clipped lower portion fof the pulse in a mannerknown in the art. The pulse (ni therefore causes the first multivibrator I to generate a positive pulse (o) which is applied to the delay network in the same manner as described heretofore with respect to thepositive pulse (e) of the transmitting networlrlA y I As explained'heretofore with respect to the operation of the multivibrator circuits in the transmitting" conditiomif the circuit falls out of synchronism. the 'various multivibrators will provide pulses at somewhatincreased time intervals until belimitedbymeausofa. A

maingpulaes wmvarymmncdv-awlhnspecttothe recdvedeobd-lash. 'lbcalrecttsuchvariathru-h the third "transmit-relllilhll ceiveswiteh|ltoa1qludnceriwillbesub somephaaedidtlmhinhnmtinthevarious understood that the signals B' derived from the third trans mit-receive" switch Il may be applied to actuan; any other desired type o! utilisation apparatus. not shown.

Signal filmer ligure 4 shows a typical wave multiplier circuit forming a portion ot both the coding wave transmitter and receiver circuits described heretoiore with reference to Figure 1 o! the drawings. This multiplier circuit is described and claimed in applicants copending U. S. application Serial No. 517.967, tiled January 12, 1944. and assigned outputvoltagewhichiaproportionaitothesquare oftheinstantaneousinputvoltageoverareasm-v ablevoltagerangeinasingiepolarity. Suchcircuitsordeviceswillbereien'edtoas circuits,"andwillbedcsignatedasQwl\crel referred to hereinafter.

In the preferred form ot the multiplying circuit. thewaves8andK,tobemultiplied,areadded together with tour diiierent polarity combimtions and squared in four diilerent signal channels. Then the tour squared signals are added together with suitable polarlties to obtain the product SK in the output circuit nl the multiplier network. as will be illustrated by the following,

equations:

Itwillbeunderstoodthatthetermninthe above equations is the D.C. bias added to the A.-C. waves to cause all 4oi! the signal amplitude variations to have the same polarity with respect to the squaring devices.

The squaring circuit illustrated employs a pluralityoismali copperoxidercctiiiersknown commercially as "variatore," Becauae oi the particular variable resistance characteristics of the Varistorf the current therethroughis substantially proportional to the square of the applied v voltage over a reasonable range of applied voltage oi a single polarity. The multiplier network Il is shown aa including a nrst triode thermionic tube i Il having its grid electrode connected to the movable contact o! the iirst transmit-receive" switch Il. whereby signals characteristic o1'l either the coding wave K or the reciprocal thereof l/K may be applied to thetube grid cathode circuit. A second thermionic tube i I3 has its grid electrode connected to the movable contact o! the second transmit-receive switch 51, whereby either the speech signals S or the o blanked, received signals SK may be applied to the tively traverse resistors Re and Ruf to provide signal (SQ-K); the signals Sv and -K'respectitv'ely traverse resistors Rio and Rn to provide signal (-S-K): and the signals -B and K traverse respectively resistors Re and Rs to provide vsignal (-S+K). Thus, at each of the four junction points, a sum of voltage is obtainedas designated in the circuit diagram. network also includ resistors Ru and R15 leading respectively rfrom points (SK) and (-S-l-K) to ground, and resistors R14 and Rie leading respectively `from points (S+K) and (-S-K) to the pomtive terminal o! the source of bias voltage which is applied through a voltage-reducing resistor Rn. An 80GO-ohm resistance has been i'ound satisfactory for the resistors Ris, R14, R15, and Ris, while 100.000-hm resistance has been taken as the value of resistors Rs, Re, R1, Re, R9, Rio, R11 and R12.

The sum voltages at the four points of the network are applied with bias voltage A and -A to four Varistors V1, Va, Va. and V4 respectively, all o! which control the current through the com- As shown, the

' wave K is clipped von mon load resistor R11 to provide th'ereacross the product output voltage SK The output across mathematically the eect of the reversed connection on these two Varistors. These tive equations show that, idealw, only the desired voltage SK is produced across the output resistor R11.

For compensating for small dissimilarities in the Varistors and other circuit elements, it has been found desirable to provide variable resistors R1 and Ra connected as voltage dividers in the anode circuits of the tubes and H3, respectively for adjusting the relative amplitudes of -S and -K.

While in the foregoing the term multiplying circuit" has been used to deilne the circuit, it will be seen that the circuit actually is a sort of modulator which is completely balanced in the sense that only the side band frequencies are produced, while th'e input frequencies and the harmonics thereof are suppressed.

The output signals SK derived from across the output resistor Ru are applied to the movable contact of the third transmit-receive" switch 6|, whereby they may be selectively applied to either the reproducer |63 or to the first mixer 63, depending upon the desired operation of the circuit oi Figure 1.

Signal reciprocal circuit The reciprocal circuitii shown in Figure 5 of the drawing is described and claimed in the copending application of Carl A. Meneley, Serial No. 484,304, filed April 23, 1943, and assigned to the same aignee as the instant application. In this circuit instantaneous reciprocal values of an applied coding wave K are obtained by both its positive cycleI and on its negative cycle to produce a substantially rectangular wave, and inwhich the wave K and th'e rectangular wave are added together with one c of them reversed in polarity, preferably after the peaks'oi' the positive and 'negative' cycles ofthe wave K have been squashed" or attened somewhat.y The circuit includes no appreciable capacitive or inductive reactances -(the blocking capacitors in the circuit presenting negligible impedance) and,`therefore,'prpvides the reciprocal A oi substantially any appliedsignal wave iorm l regardless oi its frequency components.

Referring to Figure 5, the graphV (p) represents a typical coding wave K which' is applied to the input terminals |2Iof the circuit. The graph (s) represents the reciprocal wave l/K, which is thesum .of the ilattenedwave K, represented by the graph (q), o! reversed polarity,

`and of the rectangular wave shown ingraph (r) Th'e squashed'or attened'wave (q) may beobtained by passing lthe wave (p) through av circuit that changes its resistance with a change in applied voltage. kThe rectangular wave (r) may be produced by clipping the positive and negative cycles of the wave `(q) at the voltage levels (t) and (u) respectivelyJ'or example, close to the A.'C. axis o! the signal, and then byy amplitying the clipped signal. i

Th'e wave K applied to the input terminals |2| may, if desired, beamplied by means ofan ampliiler tube |23 to provide a peak-to-peak amplitude, for example, of theorder of 60 volts, The amplified K wave then is applied through a blocking capacitor |5| anda resistor |52 to a copper oxide rectiiier unit |53 which functions as a nonlinear resistor having the propertyvof decreasing in resistance as the applied voltage increases. The resistor |52 is of high enough resistance so that th'e driving source for the non-linear resistance unit |53 is of high impedance whereby there is yonly a slight variation in the current flow through the unit |53. The unit |53 may consist of a pair of 'copper oxide'rectiilers |63a and |5812 connected to conduct current in oppositedirections.

The voltage appearing across the non-linear unit |53 is the voltage wave (q). whichl is the wave K having a iiattened wave form. This voltage, which is amplied by a cathode biased vacuum tube |54, appears across an anode resistor |56 and a portion oi the anode resistor lil-itl' o1' a second amplier tube |58.

The rectangular wave (r) is produced, in this particular example, by applying the output oi the tube |54 through a blocking capacitor I 59 and a high' impedance resistor ISI to a pair of diodes |62 and |63, which are connected to conduct in opposite directions. Resistors |64 and |66, of comparatively low resistance, are connected in series with the diodes |62 and |63, respectively. A biasing voltage drop for opposing current-now through diode |63 is produced across the resistor |86 by connecting a source of voltage (notr shown) thereacross, a' resistor Il being in rseries with the voltage source. The dlodes |82 and ISB clip the applied wave (q) symmeans of an electrical network in which the sa across the resistors its and |66, respectively.

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`rality of signal devices, apparatus for synchronizing said devices comprising means for periodically deriving predetermined signals from a first oi' said devices, means for applying s aid derived signal to generate a first signal pulse, means responsive to the termination of said iirst pulse for generating a second signal pulse of opposite polarity than said nrst pulse, means for periodically combining said rstand second pulses with signals from said first oi said devices, means for deriving control pulses in response to the periodic reversal in polarity between said rst and second pulse signal components of said combined signals, and means for periodically applying said derived control pulses to synchronize another of said devices with said iirst device.

9. In a communication system including a plurality of signal devices, apparatus for synchronizing said devices comprising means for periodically deriving predetermined signals from a first of said devices, a rst pulse generator, means for applying said derived signals to said ilrst pulse generator to generate a ilrst signal pulse, a second pulse generator, means responsive to the termination of said rst pulse for actuating said second pulse generator for generating a second signal pulse of opposite polarity than said rst pulse, means for periodically combining said iirst and second pulses with signals from said rst oi' said devices, means for deriving control pulses in reponse to the periodic reversal in polarity between said irst and second pulse signal components of said combined signals, and means ior periodically applying said derived control pulses to synchronize another of said devices with said iirst device.'

10. In a communication system including a plurality of signal devices, apparatus for synchronizing said devices comprising means for periodically deriving predetermined signals from a ilrst of said devices, a rst pulse generator, means for applying said derived signals to said rst pulse generator to generate a iirst signal pulse, a second pulse generator, means responsive to the ter. mination of said first pulse for actuating said second pulse generator for generating a second signal pulse of opposite polarity than said iirst pulse, means ior periodically combining said rst and second pulses with signals from said rst of said devices, means for transmitting said combined signals, means for receiving said combined signals, means including a dierentiating network for deriving control pulses in response to the periodic reversal in polarity between said ilrst and second pulse signal components oi said received combined signals, and means for periodically applying said derived control pulses to synchronize another o! said devices with said rst device.

11. A system oi' the type described in claim 4 including means for segregating said first and second pulses -irom said receivedsignals, and means for combining predetermined portions of the remainder of said received signals with signals derived from said other oi said devices.

12. In a communication system including a plurality of coded signal devices, apparatus ior a* pif a iirst of said devices. a iirst mul for applying said derived-i s l: itc: kayf'said nrst multivibrator toxg te ai.'iirst-f-signal-pulse,fa second multivibrator, 'means'fgespo. 5to: .the termination of saidfpulse actuatingisaid second multivibrator tovgenerate,e. secondf signal pulse oi opposite polarity. than saidfrst pulse, means for periodically- -combiningsaideilrst' and second pulses -with-codedasi i. fromzsaid first of said devices.; me z-fortransmitting said .com-i bined signals, means iorLreceivingsaid 'combined signals, meansxincluding a differentiating network for deriving contrer-pulses i inresponse to' `the periodic reversal in polarity between said ilrst and second pulse signal 'components of. said received combined signals, means-'for odically mi ing Said derived-control pulses to 'synchronize .an-

Aother of said devices .witnsaid rst. device, means generators, means responsive to said derived signals for generating a iirst pulse, means responsive to said iirst pulse for generating a second pulse of opposite polarity tosaid ilrst pulse, means for periodically combining said pulses, means for deriving control pulses in response to the periodic reversal in polarity of said combined pulses. and means for applying said derived control pulses to synchronize said second ot said generators with said iirst of said generators.

14.` A coded signal transmission system including a irst coding signal generator. a source of signals, means for combining said source of signals and said coding signals to provide a coded signal having instantaneous magnitudes proportional to the product of the corresponding instantaneous magnitudes of said source of signals and said coding signals, means responsive to predetermined signals derived from said vcoding sisnal generator for generating a ilrst pulse, means responsive to the termination of said iirst pulse for generating a second pulse, means responsive to said second pulse for keying said coding signal generator, means for combining said first and second pulses and said coded signal, means for transmitting said combined pulsed-coded signal, means for receiving said transmitted signal, means for deriving from said received signal a control pulse in response to the reversal in polarity of said lsignal pulse component, a second coding signal generator, means `responsive to said control pulse for keying said second coding signal generator to synchronize said coding signal generators, means responsive to said second coding signal generator for segregating said transmitted and received pulses from said received coded signals, means responsive to said second coding generator for deriving decoding signals having instaneous magnitudes which are substantially the reciprocal of the corresponding instantaneous magnitudes of said coding signals, means for combining said segregated coded signals and said decoding signals to derive a decoded signal having instantaneousmagnitudes substantially equal to the product of the instantaneous magnitudes 15 dehntnidlnlteanhlnndlgmllmdhm math!!! musulmanes*- Y 16 meontmlmtllllnmll mdtdlullnlnidmmhgmelm Inseam nklmtullnldnemdmb torderlvlnzemtnlpnhl-Inmtnthsn- 

